Activity 5.1: Group B Transportation
Handout
How do we get around?
People in the United States get around in many different ways – buses, cars,
trucks, bikes, trains, planes, skateboards, roller skates, skis, boats, and foot (to name a
few). Many of these forms of transportation lead to carbon dioxide emissions. In fact,
transportation emits about one third of greenhouse gas emissions in the United States
(second only to electricity generation in power plants). Most of these emissions are
related to personal cars, trucks, and plane rides, and some of these emissions are from
commercial trucks and planes.
Transportation in vehicles with combustion engines
Most emissions from transportation come from our use of cars, trucks, trains, and
airplanes with combustion engines. Most of these vehicles use non-renewable fossil
fuels like gasoline (which comes from petroleum) or natural gas, and some use
renewable resources like biofuels. Combustion engines work by burning gasoline.
Gasoline molecules have energy rich C-C and C-H bonds that contain stored potential
chemical energy. When the gasoline burns, the atoms from the gasoline molecules are
rearranged into new water and carbon dioxide molecules. When this oxidation happens,
the stored chemical energy is transformed to motion and heat energy, which make the
car run. Some engines burn biofuels or natural gas instead of gasoline, but the basic
mechanism is the same, because all of these fuels contain energy-rich C-C and C-H
bonds: these materials are burned to make the vehicles run.
Transportation in electric vehicles or hybrid vehicles
Some vehicles’ engines are powered using electricity instead of burning fossil
fuels. Most of these cars store chemical energy in batteries that can be used and then
recharged. The chemical energy in the battery is extracted, transformed into electrical
energy, which is then transformed
into motion energy that makes the
motor run. When these batteries run
out of energy, they can be
recharged.
Electric engines can still
contribute to carbon dioxide
emissions. Even though there are
no fossil fuels (like gasoline)
burning inside the engine, the
electricity that charged the battery
was generated at a power plant,
and then transported to the
charging location through cables
Human Energy Systems Unit, Activity 5.1
Carbon: Transformations in Matter and Energy
Environmental Literacy Project
Michigan State University
and wires in the “grid.” Because most power plants in the United States use coal and
natural gas to generate electricity, it is likely that the energy used to power electric cars
causes carbon emissions indirectly.
Hybrid vehicles used both combustion and electric engines. They also have an
internal generator that converts motion energy from the car (when the brake is applied)
into chemical energy that is stored in the battery.
Transportation on foot or bike (or anything human-powered).
Walking, running, riding bikes, skiing, skateboarding, or roller skating are all
forms of transportation that are powered by the chemical energy stored in our bodies.
This chemical energy is stored in the C-C and C-H bonds of high-energy molecules, like
fats and carbohydrates. When we move, cellular respiration in our bodies deconstructs
these large macromolecules and rearranges the atoms into new molecules, like carbon
dioxide and water. When the carbon atoms from the fat molecules recombine with
oxygen to form carbon dioxide, energy is released in the form of motion and heat, which
is how we move our bodies. This energy can then be used to pedal a bicycle or push a
skateboard. When we move, the carbon dioxide and water vapor that result from cellular
respiration are exhaled through our lungs, and go into the atmosphere pool. Even
though there are carbon emissions associated with these forms of transportation, the
emissions are much less than using combustion or hybrid vehicle engines.
How much carbon dioxide to
we emit when we move one
mile?
When we travel one mile
using different forms of
transportation, we emit different
amounts of carbon dioxide. The
most efficient form of
transportation in terms of carbon
dioxide emissions are walking or
biking. Some forms of public
transportation like buses and
subways that transport many
people at once are also relatively
low in carbon emissions. The
types of transportation that emit
the most carbon dioxide are
engines that require a lot of
energy to power the vehicles, like
airplanes and solo-driver cars.